The metric system is used by scientists and health professionals worldwide. A modified version of metric, called the International System of Units (SI) was adopted in 1960 to provide additional uniformity. The table below notes common units of measurement in both metric and SI:

UNITS OF MEASUREMENT
Measurement	Metric	SI
Length	Meter (m)	Meter (m)
Volume	Liter (L)	Cubic Meter (m3)
Mass	Gram (g)	Kilogram (kg)
Time	Second (s)	Second (s)
Temperature	Celsius (0C)	Kelvin (K)

Length, time and temperature are fairly self-explanatory. Volume and mass need a little more clarification. Volume measures the amount of space occupied by a substance. Think of volume as a fluid measurement, such as how much water is in a glass. Mass is a measure of the quantity of material an object contains. It may be helpful to think of mass as a measurement of weight, such as the weight of a patient. It should be noted, however, that mass is not the same as weight. Weight is the measure of gravitational pull on an object. In space, a man will weigh less than on earth but the man's mass will not change. That is why scientists measure mass instead of weight - mass does not vary.

In both metric and SI, a prefix can be attached to any unit to increase or decrease its size by some factor of 10. For example, a kilogram is equal to 1,000 grams; a milligram is equal to one-thousandth of a gram. The table below illustrates this unique feature:

METRIC AND SI PREFIXES
Prefix	Symbol	Meaning	Numerical Value	Scientific Notation
Prefixes that increase the size of a unit
mega	M	one million	1,000,000	106
kilo	k	one thousand	1,000	103
Prefixes that decrease the size of a unit
deci	d	one-tenth	0.1	10-1
centi	c	one-hundredth	0.01	10-2
milli	m	one-thousandth	0.001	10-3
micro	m	one-millionth	0.000001	10-6
nano	n	one-billionth	0.000000001	10-9

In the healthcare field, you will make changes in units everyday. For example, you may need to convert someone's weight in pounds to their weight in kilograms to calculate a proper dosage for the patient's size. Conversion factors are simple formulas that help you do this. The first table below lists measurement equivalents. The second table lists metric conversion factors and the third table lists metric-to-U.S. relationships and conversion factors.

MEASUREMENT EQUIVALENTS
Length	1 meter (m) = 100 centimeters (cm) 1 meter (m) = 1000 millimeters (mm) 1 meter (m) = 39.4 inches (in.) 1 inch (in.) = 2.54 centimeters (cm)
Volume	1 liter (L) = 1000 milliliters (mL) = 1000 cm3 1 liter (L) = 1.06 quarts (qt) 1 quart (qt) = 946 milliliters (mL)
Mass	1 kilogram (kg) = 1000 grams (g) 1 kilogram (kg) = 2.20 pounds (lb) 1 pound (lb) = 454 grams (g)
Temperature	0F = 1.8 0C + 32 0C = (0F-32)/1.8 K = 0C + 273
Gases	1 atm = 760 mm Hg 1 mole (STP) = 22.4 L
H2O	density = 1.00 g/l mL melt = 80 cal/g boil = 540 cal/g SH = 1 cal/g C
Energy	1 Cal = 1 kcal = 1000 cal 1 calorie (cal) = 4.18 joules (J)

METRIC CONVERSION FACTORS
Metric Relationship (Equality)	Conversion Factors
Length
1 m = 1,000 mm	1m and 1000 mm 1000 mm 1m
1 cm = 10 mm	1cm and 10 mm 10 mm 1cm
Volume
1 L = 1,000 mL	1L and 1000 mL 1000 mL 1L
1 dL = 100 mL	1dL and 1000 mL 100 mL 1dL
Mass
1 kg = 1,000 g	1kg and 1000 g 1000 g 1kg
1 g = 1,000 mg	1g and 1000 mg 1000 mg 1g

METRIC-U.S. RELATIONSHIPS & CONVERSION FACTORS
Relationship	Conversion Factors
Length
2.54 cm = 1 in.	2.54 cm and 1 in. 1 in. 2.54 cm
1 m = 39.4 in.	1m and 39.4 in. 39.4 in. 1m
Volume
946 mL = 1 qt.	946 mL and _1 qt. _ 1 qt. 946 mL
1 L = 1.06 qt.	1L and 1.06 qt. 1.06 qt. 1L
Mass
454 g = 1 lb.	454 g and _1 lb. 1 lb. 454 g
1 kg = 2.20 lb.	1 kg and 2.20 lb. 2.20 lb 1 kg